This application is based on, and claims priority from, Japanese Application No. HEI 2-321418 filed Nov. 26, 1990, the disclosure of which is incorporated herein by reference.
The present invention relates to the distal end portion of an endoscope of the type in which a prism for bending an optical path at a substantially right angle is disposed between an objective optical system and a solid-state image pick-up element.
It is known to utilize an endoscope in which the light receiving surface of a solid-state image pick-up element is oriented in parallel with the center axis of an objective optical system so that it does not occupy too much of the cross sectional area of the interior of the distal end of the endoscope.
FIG. 8A is a schematic illustration showing the distal end 100 of this type of conventional endoscope. As shown, the optical axis of objective optical system 101 is bent by rectangular prism 102 and reaches light receiving surface 103a of a solid-state image pick-up element 103. The shape of rectangular prism 102 is rectangular or square in cross-section when viewed from objective optical system 101, as shown in FIG. 8B.
Prism 102 thus occupies a large proportion of the cross sectional area of distal end 100 of the endoscope. Within distal end 100, the members to be contained, such as a fluid pipe and a light guide fiber bundle, are disposed in the remaining space. The result is an increase in the diameter of distal end 100 of the endoscope. If distal end 100 is of a large diameter, insertion may be difficult and uncomfortable for the patient.